The present disclosure is generally related to selective extraction of Strontium (Sr) and Barium (Ba) from sediment to determine marine or continental sedimentary environments of terrigenous elastic sediments.
Strontium (Sr) and Barium (Ba) are alkaline earth metals and exhibit similar geochemical behaviors in endogenous geological processes. However, due to differences in their chemical properties, they behave differently in exogenetic sedimentary processes. Because the differences in the geochemical environments between rivers and the sea (e.g., Eh, pH, salinity, and the concentrations of other ions), especially in estuaries where seawater and river water interact, due to the different geochemical behaviors of Sr and Ba in the ionic state in water, the result is that continental terrigenous elastic sediments are enriched in Ba, whereas marine terrigenous elastic sediments are enriched in Sr. Therefore, the Sr/Ba ratio may be used to distinguish marine or continental sedimentary environments of terrigenous elastic sediments.
At present, many sedimentary scientists and sedimentary geochemists use the Sr/Ba ratio obtained by whole-rock chemical analysis or bulk sample analysis of terrigenous elastic sediments to discriminate between marine and continental sedimentary environment, but the discrimination results may be unsatisfactory. The main reason is that the sample pretreatment methods used by most of the researchers in the analysis are inappropriate. Because the concentration of Sr and Ba measured by whole-rock analysis consists of two parts: a part is from the elastic minerals reflecting geological background information of the material source regions (structure environment rock type, weathering characteristics), and another part comes into being during sedimentary processes reflecting marine or continental sedimentary geochemical environment changes (sedimentogenic Sr and Ba).
Currently, sedimentologists and sedimentary geochemists primarily use two types of analytical methods to measure Sr and Ba in elastic sediments. The first analytical method is X-ray fluorescence spectroscopy (XRF methods, including the pressed powder pellet method and fused glass bead method), the other method is inductively coupled plasma optical emission spectrometry or inductively coupled plasma mass spectrometry (ICP-OES or ICP-MS, abbreviated as ICP methods). The XRF methods involve crushing a bulk sample to 200-mesh, pressing powder or fused glass, then measuring a bulk sample element content. The ICP methods involve crushing a bulk sample to 200-mesh, digesting all the elements in a solution, then measuring the concentrations of elements with an appropriate ICP instrument. The current most commonly used ICP methods for digesting geological samples are acid digestion (via hydrochloric acid, nitric acid, hydrofluoric acid, and perchloric acid) and fusion (lithium tetraborate or lithium metaborate fusion followed by dilute acid extraction). However, both are whole-rock chemical analysis. Using the above analytical methods, the analytical results of modern sediments represent the total amounts of Sr and Ba in the bulk samples. However, to distinguish sedimentary environments, what we need is the sedimentogenic Sr and Ba contents in elastic sediments, not the total Sr and Ba contents should be determined. A new sample pretreatment method may selectively extract the sedimentogenic Sr and Ba from terrigenous elastic sediments in order to use the Sr/Ba ratio to distinguish between marine and continental sedimentary environments.